A bridge rectifier is a type of electrical circuit in which four rectifying paths are connected between each of two alternating current (AC) input paths and each of two direct current (DC) output paths to provide the same polarity of output for either polarity of input (half wave). The rectifying paths usually include one or more diodes, which are quite inefficient and considerably affect the overall efficiency of power conversion from AC energy to DC energy. The inefficiency arises from the forward voltages of the diodes, which may be up to 1 volt or more. As at least two diodes are connected in series at any time during operation of a bridge rectifier, the voltage loss caused by the diodes may approximately be between 1.4 and 2 volts (V) in common power supply circuits with an input voltage approximately between 85 and 265 volts. In various applications, bridge rectifiers are connected upstream of further supply voltage processing circuitry such as power factor controllers, active filters or voltage regulators. Due to the nature of AC and the behavior of bridge rectifiers, the power supplied to the subsequent supply voltage processing circuitry may be unstable and vary within the input voltage range.
In order to decouple an electronic load from the voltage protection circuitry, an energy storing element like a capacitor may be used. When power is switched on (or off), unwanted artifacts like voltage and/or current peaks in the output voltage of the supply of the voltage processing circuitry may occur during transients or in an early stage. The maximum, instantaneous input current drawn by an electrical device when first turned on is commonly referred to as inrush current, input surge current or switch-on surge. Power converters often have inrush currents much higher than their steady state currents, due to the charging current of the input capacitance. The selection of overcurrent protection devices such as fuses and circuit breakers is made more complicated when high inrush currents must be tolerated. The overcurrent protection must react quickly to overload or short circuit but must not interrupt the circuit when the inrush current flows. In certain cases, this necessitates additional measures to limit the inrush currents, e.g., series resistors, which cause additional losses.